Unit IV Ultrasonic examination of welds Foreword

This part of BS 3923 differs from the previous edition of BS 3923:Part 1 in the inclusion of additional, more detailed requirements for the examination of the most common types of welded joint. These requirements are sub-divided into three Examination Levels, applicable to welds of different required levels of integrity, with specific details covering test sensitivity, test coverage and surface finish.

A fourth Examination Level is listed, the details of which should be in accordance with the general requirements of this Part of BS 3923 and agreed by the contracting parties. In addition, methods for evaluating and sizing imperfections are presented in a more detailed and formalized manner than before. In order to apply ultrasonic inspection more efficiently, an appendix giving recommendations on the parameters to be defined when setting an acceptance standard for quality control purposes has been also added.

It is emphasized that a satisfactory technique can only be determined after taking into account all the relevant factors regarding the equipment to be used and the characteristics of the weld to be examined. The use of any method should always be considered in relation to inspection and testing as a whole. The full benefits of this or any other method can only be obtained by considering the results in conjunction with those likely to be obtained from any other method.

Purchasers of ultrasonic examination services to this standard are advised to specify in their purchasing contract that the supplier operates a quality system in compliance with BS 5750 to assure themselves that examinations claimed to comply with BS 3923:Part 1 consistently achieve the required level of performance.

It has been assumed in the drafting of this British Standard that the execution of its provision is entrusted to appropriately qualified and experienced people. Compliance with a British Standard does not of itself confer immunity from legal obligations.

Personnel

The successful application of manual ultrasonic testing depends on the knowledge and experience of the personnel responsible for producing the test procedures, and the technical competence and ability of the ultrasonic practitioner to carry out the procedural requirements and interpret results. Unless otherwise agreed between the contracting parties the appropriate level and category of certification of personnel shall be in terms of those obtained from an agreed nationally accredited certification scheme.

Equipment

5.1 Flaw detector and probes Presentation A-scan presentation shall be used. The trace shall be well defined and associated with permanent graticule scale markings covering both range and amplitude Test frequency The equipment shall be capable of working at a test frequency within the range 1 MHz to 6MGHz Time base linearity The linearity of the time base shall be within 2% over the whole range, i.e. the echoes do not deviate by more than 2% of the time base range from their true position.

5.1.4 Amplifier linearity Linear The amplifier shall be linear to an accuracy of +-1 db at any point within the range 20% to 80%full screen height. The amplifier shall also have a dynamic range up to 80% full screen height of not less than 24 dB Logarithmic The amplifier shall give equally spaced decibel steps throughout the graticule height Calibrated gain control The gain shall be adjustable via a calibrated gain control having steps of not more than 2 dB and an accuracy of not less than 1 dB over any 20 dB range.

5.1.6 Probes Any internal “noise” from probes shall not interfere with the interpretation of results at the working sensitivity Resolution The resolution of the combined electronic apparatus and probe shall be measured on the A7 test block shown in BS 2704 by the method described in BS 4331:Part 3. This test block is suitable for measuring the resolution of compression wave probes and shear wave probes. Compression wave probes in the range 4 MHz to 6MHz shall clearly resolve the 3mm step and the 4mm step; lower frequency probes shall resolve the 5mm step.

Shear wave probes in the range 4MHz to 6MHz shall clearly resolve the 2mm step and the 3mm step; lower frequency probes shall resolve the 4mm step and the 5mm step. 5.2 Reference and calibration blocks Calibration blocks for routing calibration and the determination of specific probe characteristics shall be as specified in BS 2704 and BS 4331: Part 3 respectively. Reference standards to be used for setting sensitivity by means of the DAC method shall be as described in K.1.

5.3 Coupling Coupling shall be obtained by wither contact or gap scanning, using a liquid, gel or paste medium suitable for the application and compatible with the material under test. The maximum surface temperature when using conventional probes and couplants shall not exceed Calibration The method of calibration of the flaw detector and probes shall be in accordance with BS 4331: Parts 1 and 3. The probes and test block used during calibration shall be maintained at a temperature within +-15 of that of the joint to be examined.